Mating Systems

Mating Systems
Animals display a diversity of mating
systems. Behavioral ecologists generally
classify mating systems by the
degree to which males and females
associate during mating. Monogamy
is an association between one male
and one female at a time. Polygamy is
a general term that incorporates all
multiple mating systems where females
and males may have more than one
mate. Polygyny refers to a male that
mates with more than one female.
Polyandry is a system in which a
female mates with more than one
male. There are specific types of
polygyny. Resource defense polygyny occurs when males gain access to
females indirectly by holding critical
resources. For example, female bullfrogs
prefer to mate with males who
are larger and older. These males
defend territories of higher quality than
smaller males because their territories
have better temperature regimes for
tadpoles to grow or because they are
free of predatory leeches. Female
defense polygyny occurs when
females aggregate and, consequently,
are defendable. Thus, when female
elephant seals occupy a small island,
dominant males can defend and gain
access to them for mating relatively
easily (Figure 38-18). This situation
was previously known as a “harem.”

Figure 38-18 Two elephant seals, Mirounga angustirostris, fight to establish dominance.
Males are much larger than
females in this highly polygynous society.

Male dominance polygyny occurs
when females select mates from aggregations
of males. For example, some
animals form leks. A lek is a communal
display ground where males congregate
to attract and court females.
Females choose and mate with the male having the most attractive qualities
(Figure 38-19). Leks characterize
some birds, including prairie chickens
and sage grouse. In these systems, sexual
selection is often intense,
resulting in evolution of bizarre
courtship rituals and exaggerated morphological
traits.